The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
During the combustion process, gasoline is oxidized and hydrogen (H) and carbon (C) combine with air. Various chemical compounds are formed including carbon dioxide (CO2), water (H2O), carbon monoxide (CO), nitrogen oxides (NOx), unburned hydrocarbons (HC), sulfur oxides (SOx), and other compounds.
Automobile exhaust systems include a catalytic converter that reduces exhaust emissions by chemically converting the exhaust gas into carbon dioxide (CO2), nitrogen (N), and water (H2O). Exhaust gas oxygen sensors generate signals indicating the oxygen content of the exhaust gas. An inlet or pre-catalyst oxygen sensor monitors the oxygen level associated with an inlet exhaust stream of the catalytic converter. This inlet O2 sensor is also the primary feedback mechanism that maintains the air-to-fuel (A/F) ratio of the engine at the chemically correct or stoichiometric A/F ratio that is needed to support the catalytic conversion processes. An outlet or post-catalyst oxygen sensor monitors the oxygen level associated with an outlet exhaust stream of the catalytic converter. The post-O2 sensor signal is used for secondary A/F ratio control.
Engine diagnostic systems require properly functioning oxygen sensors. Therefore, the oxygen sensors are periodically checked to ensure proper function. Traditionally, the diagnostic systems employ intrusive checks to check the operation of the sensors. During the intrusive checks, the A/F ratio may be manipulated and the sensor response is monitored. However, these intrusive checks may increase exhaust emissions and/or cause engine instability and reduced drivability that may be noticeable to a vehicle operator.
During some operating conditions, an engine control system may cutoff fuel to the engine during deceleration. This technique is often referred to as deceleration fuel cutoff (DFCO). Some diagnostic systems evaluate operation of the post-catalyst oxygen sensor during DFCO.